The present invention relates to medical systems and more particularly to medical fluid treatment therapies.
Due to disease, injury or other causes, a person's renal system can fail. In renal failure of any cause, there are several physiological derangements. The balance of water, minerals and the excretion of daily metabolic load are reduced or no longer possible in renal failure. During renal failure, toxic end products of nitrogen metabolism (e.g., urea, creatinine, uric acid, and others) can accumulate in blood and tissues.
Kidney failure and reduced kidney function have been treated with dialysis. Dialysis removes waste, toxins and excess water from the body that would otherwise have been removed by normal functioning kidneys. Dialysis treatment for replacement of kidney functions is critical to many people because the treatment is life sustaining. One who has failed kidneys could not continue to live without replacing at least the filtration functions of the kidneys.
Hemodialysis (“HD”), hemofiltration (“HF”), hemodiafiltration (“HDF”) and peritoneal dialysis (“PD”) are types of dialysis therapies generally used to treat loss of kidney function. Peritoneal dialysis utilizes a sterile dialysis solution, or “dialysate”, which is infused into a patient's peritoneal cavity and into contact with the patient's peritoneal membrane. Waste, toxins and excess water pass from the patient's bloodstream through the peritoneal membrane and into the dialysate. The transfer of waste, toxins, and excess water from the bloodstream into the dialysate occurs due to diffusion and osmosis during a dwell period as an osmotic agent in the dialysate creates an osmotic gradient across the membrane. The spent dialysate is later drained from the patient's peritoneal cavity to remove the waste, toxins and excess water from the patient.
Hemodialysis treatment removes waste, toxins and excess water directly from the patient's blood. The patient is connected to a hemodialysis machine and the patient's blood is pumped through the machine. Needles or catheters are inserted into the patient's veins and arteries to create a blood flow path to and from the hemodialysis machine. As blood passes through a dialyzer in the hemodialysis machine, the dialyzer removes the waste, toxins and excess water from the patient's blood and returns the cleansed blood back to the patient. A large amount of dialysate, for example about ninety to one hundred twenty liters, is used by most hemodialysis machines to dialyze the blood during a single hemodialysis therapy. Spent dialysate is discarded. Hemodialysis treatment lasts several hours and is generally performed in a treatment center about three times per week.
Hemofiltration is an effective convection-based blood cleansing technique. Blood access can be venovenous or arteriovenous. As blood flows through the hemofilter, a transmembrane pressure gradient between the blood compartment and the ultrafiltrate compartment causes plasma water to be filtered across the highly permeable membrane. As the water crosses the membrane, it convects small and large molecules across the membrane and thus cleanses the blood. A large amount of plasma water is eliminated by filtration. Therefore, in order to keep the body water balanced, fluid must be substituted continuously by a balanced electrolyte solution (replacement or substitution fluid) infused intravenously. This substitution fluid can be infused either into the arterial blood line leading to the hemofilter (predilution), into the venous blood line leaving the hemofilter (postdilution) or both. Another type of therapy, hemodiafiltration, combines the diffusion and convective cleansing modes of hemodialysis and hemofiltration.
A patient's hematocrit, which is the percentage of red blood cells in the blood, is about thirty-two to thirty-six percent by volume, leaving the amount of fluid in the blood to range from about sixty-four to sixty-eight percent. In a typical HDF and HF therapy, blood flow can be about 300 ml/min, wherein about 100 ml/min of the fluid is being removed through the filter, leaving a relatively smaller percentage of the blood as fluid to exit the hemofilter and to thereafter receive an amount of dialysate.
Postdilution is a more efficient blood clearance mode than predilution HF or HDF. In some instances, postdilution HF or HDF can be fifty percent more efficient than predilution HF or HDF. With postdilution clearance, however, blood exits the body and enters the filter before the extracorporeal circuit receives therapy fluid or dialysate. Because the hemodialyzer or hemofilter can remove a good portion of the liquid from the patient's blood, postdilution clearance can hemoconcentrate or clot the blood filter. Predilution clearance, on the other hand, infuses fresh therapy fluid into the extracorporeal circuit before the filter and therefore at least substantially reduces the possibility that blood will clot in the hemofilter or hemodialyzer.
With predilution HF or HDF, the dialysate is fed into the extracorporeal circuit prior to the hemofilter. Some of that fluid is then immediately removed by the filter, rendering the therapy less effective than postdilution therapy. Blood leaving the filter, however, has the same percentage liquid, e.g., sixty-four to sixty-eight percent, as the blood leaving the patient, reducing the chances of clotting or aggregating blood platelets because the blood has too high a percentage of solids.
It is therefore desirable to provide a hemofiltration and/or a hemodiafiltration system that can perform both predilution or postdilution clearance modes.
It is also desirable to provide an HF and/or an HDF system that provides a priming function, bolus infusion function and/or a blood rinseback function. System priming occurs at the beginning of therapy to remove air from the line, which would be harmful if delivered to the patient. The prime purges the air with a sterile or substantially sterile electrolyte solution.
At certain times during HF or HDF therapy it is necessary to deliver a bolus or relatively large volume of fluid to the patient. It may happen during therapy that too much blood is removed from the patient too quickly. The patient's vascular space contains only five to six liters of blood. Removing too much blood too quickly can possibly lower the pressure in the vascular space. The patient's heart rate will quicken and the vascular system will contract in an attempt to compensate for the loss in blood pressure, however, such measures may not be enough to prevent the patient from becoming hypotensive. In such a case, providing a bolus or volume of fluid to the patient is one effective procedure for increasing the blood pressure in the vascular system.
It is further desirable to have an HF or HDF system that can provide a blood rinseback at the end of therapy. At the end of therapy there is typically blood that remains in the extracorporeal circuit. It is desirable to return as much of that blood as possible to the patient. To do so, the blood therapy system needs to have the ability to pass a volume of fluid through the blood circuit sufficient to push the blood remaining therein back to the patient.
Both the bolus feature and the rinseback feature present challenges to the machine manufacturer. For instance, if the machine uses a fluid balancing system or match flow equalizer that removes an equal amount of fluid from the patient for each amount of fluid delivered to the patient, that balancing system must be accounted for to enable a positive net fluid volume to be delivered to the patient. Second, since the fluid is delivered directly to the extracorporeal circuit, the bolus or rinseback fluid needs to be sterile or of an injectable quality.
Removing ultrafiltrate (“UF”) from the patient is a precise operation in which a specific amount of fluid needs to be removed from the patient over the course of therapy. The amount of fluid removed from the patient therefore needs to be carefully monitored. In that regard, problems arise if the device or devices controlling the UF rate or volume output fails, e.g., if a valve fails. In such a case, uncontrolled flow from the patient can occur causing an overfiltration of the patient. It is therefore desirable to have an ultrafiltration flow control device that fails in such a way that fluid flow is blocked and uncontrolled UF removal does not occur.
Certain HF and HDF machines generate the fluid used during therapy at the time and place that the therapy takes place. Those machines are referred to as “on-line” machines because they make and provide the solution on-line. On-line machines use micro or ultrafilters to sterilize the solution or make it of an injectable quality before the solution is delivered to the patient's extracorporeal circuit. The filters over time accumulate bacteria and endotoxin along the outer filtering surfaces of the membranes located inside the filters. It is therefore desirable to have a method and apparatus that cleans or at least reduces the amount of bacteria and endotoxin that accumulate and reside along the membranes of the filters used to create dialysate on-line.